Traffic control system and apparatus

ABSTRACT

AN IMPROVED APPARATUS IS PROVIDED FOR USE IN A TRAFFIC CONTROL SYSTEM OF THE TYPE WHEREIN THE TRAFFIC CYCLE LENGTH IS DETERMINED BY THE TIME BETWEEN ADJACENT PHASE COINCIDENCES OF TWO WAVE ENERGIES, ONE OF WHICH IS GRADUALLY SHIFTING IN PHASE WITH RESPECT TO THE OTHER. THE IMPROVED APPARATUS IS ADAPTED TO SUBDIVIDE EACH TRAFFIC CYCLE, IN TIME, AND MAY BE USED TO TRIGGER COMMAND SIGNALS TO OCCUR AT PREDETERMINED PERCENTAGE POINTS OF THE CYCLE.

United States Patent Inventor Appl. No.

Filed Patented Assignee Charles L. DuVivier Darien, Conn.

Jan. 27, 1969 June 28, I971 LFE Corporation Waltham. Mass.

TRAFFIC CONTROL SYSTEM AND APPARATUS 7 Claims, 5 Drawing Figs.

u.s. Cl. 340/40 m. or 608g 1/01 ma of Search 340/40 Primary Examiner- William C. Cooper Attorney-Kane, Dalsimer, Kane, Sullivan and Kurucz ABSTRACT: An improved apparatus is provided for use in a traffic control system of the type wherein the traffic cycle length is determined by the time between adjacent phase coincidences of two wave energies, one of which is gradually shifting in phase with respect to the other. The improved apparatus is adapted to subdivide each traffic cycle, in time, and may be used to trigger command signals to occur at predetermined percentage points of the cycle.

TIME

Patented June 28, 1971 3 Shoots-Shoot 2 I I l I I I I l I l I l I I IIL ATTORNEYS Patented June 28, 1971 3 Shasta-Shoot 5 BY 14., M, a M v M ATTORNEYS TRAFFIC CONTROL SYSTEM AND APPARATUS BACKGROUND OF THE INVENTION In traffic control systems, the right of way between intersecting or otherwise conflicting paths of traffic is ordinarily sequentially accorded to one traffic path and then subsequently to the remaining path or paths before returning to the original path. The total time that elapses from the moment the rightof way is first granted to an initial path until it returns to that path is referred to as the traffic cycle length and is generally of the order of 40 to 150 seconds.

The trafiic cycle length is often timed by a cycle generator such as that disclosed and claimed in the currently pending U.S. application Ser. No. 777,224 filed Nov. 20, 1968 which generates and then measures the time lapse between the phase coincidence of two' wave energies, one of which is gradually shifting in phase with respect to the other. Such cycle generators are well known and widely used by'traffic control engineers. The information from a single cycle generator may be transmitted to several local controllers thus bringing them into synchronization with one another in the sense that the duration of the traffic cycle length of each of the local controllers will be the same. The various individual controllers may, however, and usually do displace the time at which the zero point of the local traffic cycle occurs with respect to the zero point generated by the cycle generator. This displacement which may be expressed as a percentage of the traffic cycle length is known as the offset and the point in time with respect to the cycle generators zero at which the offset occurs is known as the offset point.

If the traffic cycle length is considered as being 100 percent of the time lapse between adjacent phase coincidences of the wave energies generated by the cycle generator and the offset point" is considered the local zero" point, the points in time, within the local time cycle at which various command functions occur, as for example the switching of right of way between conflicting paths of traffic, may be expressed as a percentage of the local traffic cycle. Thus, it is particularly useful to be able to divide the local traffic cycle into percentage parts and to provide means for generating command signals to occur at any particular percentage point in the traffic cycle, especially if these commands may be made to occur at predetermined percentage points, regardless of the length of the traffic cycle.

Heretofore, traffic control equipment has been provided to serve the aforementioned functions; however, such prior art equipment has relied on mechanical and electromechanical components including motors and various drives which require periodic maintenance, repair and replacement of worn parts to operate within the required degree of accuracy necessary for traffic control purposes. Further, such devices are adversely affected by changes in weather conditions, and are costly and time consuming to repair and replace.

SUMMARY OF THE INVENTION It is, therefore, the principal object of the present invention to provide an improved apparatus for use in a traffic control system which utilizes all solid state electronic components to subdivide in time the traffic cycle length generated by a cycle generator adapted to provide two wave energies, one of which gradually shifts in phase relative to the other wherein the phase coincidence of the two wave energies determines the length in time of the traffic cycle.

Another object is to provide such an apparatus with standby means for generating the command signals in the event of a malfunction in the associated cycle generator.

These and other beneficial objects and advantages are attained in accordance with the present invention by providing an apparatus referred to as a "coordinator" adapted to receive two wave energies of substantially the same frequency from a cycle generator. One of the wave energies, referred to as the cycle wave, gradually shifts in phase with respect to the other wave herein referred to as the reference wave. The reference wave energy is initially displaced by a fixed percentage of the cycle length to establish the local offset or zero point. This wave is then used to trigger a pulse generator the frequency of which is a predetermined multiple of the frequency of the reference wave. The coincidence of the output of the pulse generator with the cycle wave is then used to advance a recycling multiposition counter which is adapted to generate command signals to the local controller each time it reaches predetermined positions in its count. The counter is provided with means adapted to synchronize the counter zero advance pulse with the offset pulse thereby insuring the synchronization of the command signals with the local traffic cycle, which in turn is related to the cycle generated by the cycle generator.

The coordinator is also adapted to provide standby advance pulses to the counter which in turn will trigger the necessary command signals to the local controller independently of the cycle generator in the event of a malfunction or breakdown of the cycle generator.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. 1 is a plan view of a simple intersection that may be controlled by a traffic control system of the type depicted in FIG. 2;

FIG. 2 is a block diagram of a traffic control system utilizing the coordinator of the present invention;

FIG. 3 is a block diagram of the traffic coordinator comprising the present invention;

FIG. 4 is including subfigures 4(a) through 40') schematically illustrate the pulse and wave forms developed in the traffic coordinator'of the present invention; and,

FIG. 5 is a block diagram illustration of the standby circuitry of the coordinator of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention is illustrated in the accompanying FIGS. wherein similar components are indicated by the same reference numerals throughout the several views. Reference is now made in particular to FIG. 1 wherein an intersection comprising two crossing roadways in shown. For simplification, one roadway, A" is assumed to extend between east and west and the other roadway, B," between north and south. A traffic signal 10 which may comprise one or more groups of traffic lights is provided at the intersection and controls the correlative motion of vehicles and pedestrians entering into the intersection defined by arteries A and B." In addition to affording the right of way of vehicles along roadways A and B," the traffic signal 10 may also be adapted to provide for left turns from either of the roadways onto the other, as shown by the dashed arrows.

The traffic signal 10, in turn, comprises a portion of the traffic control system 12 illustrated in FIG. 2. Traffic control system 12 includes a cycle generator 14 which receives input information relating to the desired traffic cycle length from a selector 16 and adapted to generate suitable signals corresponding to the chosen time cycle to one or more local controllers 18. through their associated coordinators 20 and offset displacers 22. As shown, the traffic cycle selector 16 may be manually operated or the selector input may come from computer 24 which in turn receives information from road detectors or other means relating to current traffic conditions. A local controller may be positioned along each of arteries A and B; at their intersection, as shown; or in some other convenient location, and serves to provide the sequential green, yellow, and red traffic signals which control the flow of traffic along the roadways or into the intersection.

The offset displacer 22 determines the zero point of the local time cycle relative to the zero of the traffic cycle. Such displacers are well known and defined in the prior art as for example in U.S. Pat. No. 2,989,728 and serve to displace the local zero for a particular controller. The local coordinator 20 accords fixed percentage limits in the traffic cycle to the various phases of traffic associated with the intersection. The local controller allocates time to each phase and subdivides each phase into the various vehicular and pedestrian intervals within these limits.

It might be noted that the function of the local controller 18 and local coordinator 20 may be contained in one unit.

In this regard, a simple two phase traffic pattern might consist of alternating the right of way between traffic on the A roadway and then along the B roadway. The offset displacer 22 would thus determine when in the master trafiic cycle (that is, the cycle generated by the cycle generator 14) the right of way would be accorded to one path of traffic as for example, along the A" roadway and then the coordinator 20 would determine at what point in the local traffic cycle the right of way should be taken away from traffic along the "A" artery and accorded to traffic along the "B" artery. The local controller 18 might, for example, divide the A" and 8" phases into pedestrian and vehicle portions. Additional traffic phases could consist of permitting left turn traffic into one or both of the A" and 8" roadways while arresting conflicting straight through and turning traffic in the other roadway. The maximum duration of each of these phases would be determined by the coordinator 20 as a percentage of the local traffic cycle. Thus, in the above example, if the total trafiic cycle length wave 120 seconds, 40 percent or 48 seconds might be allocated for A" phase traffic (along the A" roadway); 35 percent or 42 seconds might be allocated to 8" phase traffic; and the remaining 25 percent on 30 seconds TO A "C which might, for example, consist of left turns from either direction along the B" roadway to the A roadway while straight through traffic on the A" and 8" roadways is stopped. In more sophisticated traffic control systems, traffic detectors can be utilized along the roadway to determine whether or not a particular traffic phase is required, and if so, to permit the local controller to provide for that phase, while if not, to pass on to the next phase. The coordinator 20 thus serves to allocate portions of each traffic cycle to each of the various conflicting phases of traffic while the controller 18 serves to provide the necessary command signals to the traffic signal during each phase.

For purposes of this preferred embodiment, it will be assumed that the cycle generator 14 of the traffic control system 12 is of the type disclosed in the currently pending U.S. application Ser, No. 777,224 filed Nov. 20, 1968 for a CYCLE GENERATOR FOR A TRAFFIC CONTROL UNIT. This cycle generator produces two single phase sinusoidal wave energies, one ofwhich is referred to as the cycle wave which is adapted to shift in phase with respect to the other wave energy which is referred to as the reference wave. The reference wave is a 400 Hz. sinusoidal wave while the cycle wave is substantially 400 Hz. Reference is now made to FIG. 3. As was previously mentioned, the traffic cycle length generated by the cycle generator 14 represents the time between adjacent phase coincidences of the reference and cycle wave energies 28 and 26, respectively. The local offset point, that is, the zero point of the local traffic cycle may be obtained by shifting the zero point of the reference wave 28 which will cause a corresponding shift in the point in each cycle at which coincidence between the reference wave and cycle wave occurs. This way be effected by picking off a particular value of the varying reference wave energy or in any one of several methods known to traffic engineers as for example the methods disclosed in U.S. Pat. No. 2,989,728 issued on June 20, 1961 for TRAFFIC AND OTHER CONTROL SYSTEM. This properly offset reference signal 30 which is still a 400 Hz. signal, although now a pulse train, is then fed into a 40 kHz. oscillator or pulse generator 32 through the automatic frequency control circuit 34. The output 36 of oscillator 32 is thus a signal, the frequency of which is exactly I00 times the frequency of the offset reference signal 30. The automatic frequency control circuit 34 provides for correcting the frequency of the 40 kHz. oscillator in the event the reference wave 28 or the offset reference signal 30 is not precisely 400 Hz. The output 36 of the oscillator 32 forms a straight input to AND gate 38. An additional straight input 40 to AND gate 38 is the output of pulse shaper 42, the input of which is the cycle wave energy 26 which, it should be recalled, is gradually shifting in phase with respect to the reference wave energy 28. The pulse train 40 comprising the output of pulse shaper 42 will thus also gradually shift in phase with respect to the offset reference signal 30 and also the output 36 of the oscillator 32. An inhibit input 44 to AND gate 38 forms the output of the failure detector 46 which is adapted to detect any malfunction in the cycle generator which would result in a failure of either the cycle wave energy 26 or the reference wave energy 28. Thus, the inhibit input 44 is energized only in the event that there is a failure in the output of the cycle generator 14 and the failure detector mechanism 46 has been triggered. In the event there is no failure in the output of the cycle generator 14, an output 48 of AND gate 38 will occur each time there is coincidence of the output 40 of pulse shaper 42 and the output 36 of oscillator 32. This will occur I00 times as the cycle wave shifts through 360 of phase angle or times per traffic cycle since the time required for the cycle wave to shift through 360 of phase angle is the cycle length. This results in 100 coincidence pulse per traffic cycle which will appear as outputs 48 ofAND gate 38.

Reference will now be made to FIG. 4 wherein the various signals discussed above are graphically represented. Thus, in FIG. 4a the 400 Hz. reference wave 28 generated by the cycle generator 14 is depicted. In FIG. 4b the cycle wave energy 26 is depicted at various times T0, TI, and T2 in a traffic cycle. The offset reference signal 30 is depicted in FIG. 40. It can also be seen that signal 30 is of the same frequency as the 400 Hz. reference wave 28 although displaced somewhat from the zero point of the reference wave. The output 36 of oscillator 32 is shown on line 4d as I00 pulses that occur between adjacent offset reference signals 30. The output of pulse shaper 42 is depicted on line 4e. As can be seen, the output 40 of pulse shaper 42 will shift in phase in the same manner that the cycle wave shifts. The output 48 of AND gate 38 represents coincidences of the output 40 of the pulse shaper 42 and a pulse 36 which is the output 36 of oscillator 32. Thus, as cycle wave 40 shifts through 360 of phase angle, it will coincide with each of the pulses 36 and hence there will be 100 coincidence pulses 48 for each complete traffic cycle.

In FIG. 40') the coincidence of the output 40 of pulse shaper 42 with the output 36 of oscillator 32 is diagrammatically illustrated in exaggerated form. Thus, within each 2.5 millisecond interval (which represents the period between adjacent pulses 30), there will be a train of I00 pulses 36. During each complete cycle (which may vary between 40 and seconds) the cycle wave pulses 40 will shift through 360 of phase angle with respect to the reference wave pulses 30. Thus, as the cycle wave pulse gradually shifts, it will successively coincide with each of the I00 pulses generated by the oscillator 32 so that during the course of a complete cycle, there would be 100 coincidences of the pulses 40 with the pulses 36 regardless of the length of the cycle. Of course, these subsequent coincidences would not take place during each successive 2.5 millisecond interval but rather would occur in intervals related to the traffic cycle. Thus, for a 50 second cycle, two coincidences would occur each second while for a 100 second cycle one coincidence would occur per second. The rate of coincidence is, of course, directly related to the speed at which the cycle wave shifts through 360 of phase angle.

Referring again to FIG. 3, it may be seen that the coincidence pulses 48 serve to advance the 100 position counter 50 through OR gates 52 and 54 and AND gate 56. In this regard, the coincidence pulses 48 are fed to AND gate 56 through OR gate 52. The output 58 of OR gate 52 comprises a straight input to AND gate 56. An inhibit input 60 to AND gate 56 comprises the zero position of the 100 position counter 50. Thus, all the advance pulses 62 to counter 50 are derived from the coincidence gate 38 with the exception of the zero" position advance pulse which is prevented from ad vancing counter 50 by the inhibit signal 60 on AND gate 56. The zero position advance pulse is derived from the offset reference signal 30 and thus insures the synchronization of the 100 position counter 50 with the cycle generator 14. That is, the zero position advance pulse will always occur at the offset point. In this regard, the zero position pulse serves to inhibit AND gate 56 and also serves as one input to AND gate 64. An additional input 66 to AND gate 64 comprises the output of OR gate 52 and a third input 68 to AND gate 64 comprises the output of OR gate 70 which in the absence of a triggering of the failure detector 46 would comprise the offset reference signal 30. Thus, the zero position advance pulse to counter 50 comprises the output 72 of AND gate 64 which, in turn, occurs only when there is coincidence of the offset reference signal 30 with a coincident pulse 48 from AND gate 38 at a time when the 100 position counter 50 is in its zero position.

In the event of a failure or breakdown of the cycle generator 14, standby equipment 74 independent of the cycle generator is provided to supply the necessary advance pulses 62 to counter 50. The standby equipment 74, depicted in FIG. 5, includes a pulse former 76 which receivesas its input 78 a 60 Hz. AC power supply line which is readily available in most cations. The output 80 of pulse former 76 is a train of short duration pulses emanating at the rate of 60 pulses per second. The pulses 80 are used to advance a multiple position counter 82, the output of which forms one input 84 to AND gate 86. The other input to AND gate 86 is the output 88 of traffic cycle selector 90 which has inputs which may be made to correspond to any level of the counter 82 and cause the counter to stop at that point and reset to repeat its counting. Thus, counter 82 and the selector 90 cooperate in defining a variable counter that counts up to a number predetermined by properly controlling the input to selector 90. When the counter 82 reaches the predetermined level chosen, an output signal 92 will emanate from AND gate 86 which serves to reset counter 82 and as an alternate advance signal for counter 50. Since the total traffic cycle consists of 100 advance pulses to counter 50, by properly choosing the cutoff level for counter 82 virtually any desired traffic cycle length may be obtained. An offset may be developed for standby operation by running counter 50 to'zero and then delaying further advance for a suitable period of time. The logic required for this will be obvious to anyone skilled in the art. Thus, for example, assume that a 100 second cycle were desired. The 100 position counter would have to advance through all of its positions in 100 seconds or one position per second. To do this would require one output 92 from AND gate 86 per second which may be obtained by setting the cutoff of counter 82 at 60. Thus, since it will take counter 82 one second to count to 60, there will be one output pulse 92 every second, and this output pulse 92 would serve to advance counter 50 at the rate of one advance per second. Similarly, if a 50 second traffic cycle were desired, the 100 position counter would have to advance at the rate of two positions per second so that the cutoff for counter 82 should be set at 30, thereby providing two output pulses 92 per second as required.

The standby equipment 74 is triggered into action by a suitable signal on lead 94 in the event the failure detector 56 determines a malfunction in the cycle generator 14. At the same time, the failure detector 46 would inhibit AND gate 38 through lead 44 and simultaneously provide one input 96 to AND gate 98, the other input to AND gate 98 is the output 92 of the standby circuit 74. With the inhibit signal 44 on AND gate 38, the cycle generator 14 is effectively isolated from affecting counter 50. The output 100 of AND gate 98 serves as an alternate input to OR gate 52. Since the AND gate 38 would be inhibited in the event of a breakdown of the cycle generator, the input 100 to OR gate 52 would comprise the only now it would receive its signals from the standb circuit 74. The failure detector 46 also provides an input on ead 102 to OR gate 70, thus providing for output 68 from OR gate 70 to provide the necessary zero advance 72 to counter 50.

The output or outputs 104 of counter 50 may be taken at any position of the counter, each successive position representing a percentage of the traffic cycle. This output serves to provide command signals to local controller 18. Thus, in accordance with the above disclosure, an improved device for use with a traffic control system is provided which effectively subdivides the local traffic cycle regardless of the length of the cycle.

lclaim:

1. An apparatus for subdividing in time the period generated by a cycle generator of the type adapted to generate two sinusoidal electrical waves one of which gradually shifts in phase with respect to the other which may be considered stationary in phase, wherein the time period is determined by adjacent phase coincidences of the two waves, said apparatus comprising:

means for generating a train of pulses the frequency of which is a predetermined multiple of the frequency of said stationary wave;

means for comparing said pulse train with said gradually shifting wave and for generating an advance signal to a multiposition counter each time coincidence occurs between a pulse of said pulse train and a predetermined point in each cycle of said shifting wave; and

a recycling multiposition counter having a plurality of positions, said plurality being equal to the multiple said pulse train frequency is of said stationary wave frequency wherein said counter is adapted to be advanced by said comparison means advance signals whereby to subdivide said time period into a number of positions equal to said multiple.

2. The invention in accordance with claim 1 wherein said apparatus is adapted for use in a traffic control system and serves to provide command signals to a local traffic controller as said counter advances through predetermined positions.

3. The invention in accordance with claim 1 wherein said means for generating said pulse train is triggered by said stationary wave.

4. The invention in accordance with claim 3 wherein the means for generating said pulse train includes a pulse generator and the output frequency of said pulse generator is controlled by automatic frequency control means whereby to insure that the frequency of pulses of said pulse generator is said predetermined multiple of the frequency of said stationary wave.

5. The invention in accordance with claim 1 further comprising means for synchronizing the advancement of said counter with the period generated by said cycle generator including means for advancing said recycling counter through each zero position by a signal generated by said cycle generator at the start of said period.

6. The invention in accordance with claim 1 further provided with means for detecting a malfunction in said cycle generator and for providing standby advance pulses to said counter in the event of a malfunction in said signal generator.

7. The invention in accordance with claim 6 wherein said means for providing standby pulses to said multiposition counter includes a second multiposition counter adapted to be advanced during each cycle of a 60 Hz. power supply and control means for preselecting the maximum position of said counter whereby each time said second counter reaches said preselected maximum position an advance pulse is generated to said recycling multiposition counter. 

